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Modulation of force below 1 Hz: age-associated differences and the effect of magnified visual feedback.

Fox EJ, Baweja HS, Kim C, Kennedy DM, Vaillancourt DE, Christou EA - PLoS ONE (2013)

Bottom Line: Older adults demonstrated a greater increase in the variability of force with magnification of visual feedback compared with young adults (P = 0.05).Furthermore, older adults exhibited differential force modulation of frequencies below 1 Hz compared with young adults (P<0.05).Specifically, older adults exhibited greater normalized power from 0-0.16 Hz and lesser normalized power from 0.66-0.83 Hz.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, USA.

ABSTRACT
Oscillations in force output change in specific frequency bins and have important implications for understanding aging and pathological motor control. Although previous studies have demonstrated that oscillations from 0-1 Hz can be influenced by aging and visuomotor processing, these studies have averaged power within this bandwidth and not examined power in specific frequencies below 1 Hz. The purpose was to determine whether a differential modulation of force below 1 Hz contributes to changes in force control related to manipulation of visual feedback and aging. Ten young adults (25±4 yrs, 5 men) and ten older adults (71±5 yrs, 4 men) were instructed to accurately match a target force at 2% of their maximal isometric force for 35 s with abduction of the index finger. Visual feedback was manipulated by changing the visual angle (0.05°, 0.5°, 1.5°) or removing it after 15 s. Modulation of force below 1 Hz was quantified by examining the absolute and normalized power in seven frequency bins. Removal of visual feedback increased normalized power from 0-0.33 Hz and decreased normalized power from 0.66-1.0 Hz. In contrast, magnification of visual feedback (visual angles of 0.5° and 1.5°) decreased normalized power from 0-0.16 Hz and increased normalized power from 0.66-1.0 Hz. Older adults demonstrated a greater increase in the variability of force with magnification of visual feedback compared with young adults (P = 0.05). Furthermore, older adults exhibited differential force modulation of frequencies below 1 Hz compared with young adults (P<0.05). Specifically, older adults exhibited greater normalized power from 0-0.16 Hz and lesser normalized power from 0.66-0.83 Hz. The changes in force modulation predicted the changes in the variability of force with magnification of visual feedback (R(2) = 0.80). Our findings indicate that force oscillations below 1 Hz are associated with force control and are modified by aging and visual feedback.

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The interaction of age and frequency bins below 1 Hz.A: The absolute power during the three different visual angles. The age×visual angle approached significance (P = 0.06) and suggests that power within 0–1 Hz was greater in older adults for the visual angles that magnified the visual feedback. B: The normalized power for young and older adults at different frequency bins. On average, compared with young adults, older adults exhibited greater normalized power from 0–0.16 Hz and lower normalized power from 0.5–0.83 Hz. Post hoc analysis, indicates that these differences were statistically significant (P<0.05) between young and older adults at 0 Hz and 0.66 Hz. Asterisk (*) indicates significant difference (P<0.05) between young and older adults.
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pone-0055970-g005: The interaction of age and frequency bins below 1 Hz.A: The absolute power during the three different visual angles. The age×visual angle approached significance (P = 0.06) and suggests that power within 0–1 Hz was greater in older adults for the visual angles that magnified the visual feedback. B: The normalized power for young and older adults at different frequency bins. On average, compared with young adults, older adults exhibited greater normalized power from 0–0.16 Hz and lower normalized power from 0.5–0.83 Hz. Post hoc analysis, indicates that these differences were statistically significant (P<0.05) between young and older adults at 0 Hz and 0.66 Hz. Asterisk (*) indicates significant difference (P<0.05) between young and older adults.

Mentions: For the absolute power spectrum, the age×visual feedback angle interaction approached significance (F2,24 = 3.1, P = 0.06; Figure 5A). Visual inspection of the data demonstrated that magnification of visual feedback increased power below 1 Hz in older adults and decreased power below 1 Hz for young adults. The age main effect (P = 0.68) and the age×frequency bin interaction were not significant (P = 0.82). For the normalized power spectrum of force, there was a significant age×frequency bin interaction (F6, 108 = 2.59, P<0.05; Figure 5B). The interaction indicated that older adults compared with young adults exhibited greater relative power from 0 to 0.16 Hz and lesser relative power from 0.66 to 0.83 Hz under all visual feedback conditions. Post hoc analyses indicated that older adults compared with young adults exhibited greater power at 0 Hz (/t18/ = 2.6, P<0.01) 0.16 Hz (/t18/ = 1.5, P = 0.07) and lesser power from 0.66 Hz (/t18/>1.9, P<0.05).


Modulation of force below 1 Hz: age-associated differences and the effect of magnified visual feedback.

Fox EJ, Baweja HS, Kim C, Kennedy DM, Vaillancourt DE, Christou EA - PLoS ONE (2013)

The interaction of age and frequency bins below 1 Hz.A: The absolute power during the three different visual angles. The age×visual angle approached significance (P = 0.06) and suggests that power within 0–1 Hz was greater in older adults for the visual angles that magnified the visual feedback. B: The normalized power for young and older adults at different frequency bins. On average, compared with young adults, older adults exhibited greater normalized power from 0–0.16 Hz and lower normalized power from 0.5–0.83 Hz. Post hoc analysis, indicates that these differences were statistically significant (P<0.05) between young and older adults at 0 Hz and 0.66 Hz. Asterisk (*) indicates significant difference (P<0.05) between young and older adults.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3569433&req=5

pone-0055970-g005: The interaction of age and frequency bins below 1 Hz.A: The absolute power during the three different visual angles. The age×visual angle approached significance (P = 0.06) and suggests that power within 0–1 Hz was greater in older adults for the visual angles that magnified the visual feedback. B: The normalized power for young and older adults at different frequency bins. On average, compared with young adults, older adults exhibited greater normalized power from 0–0.16 Hz and lower normalized power from 0.5–0.83 Hz. Post hoc analysis, indicates that these differences were statistically significant (P<0.05) between young and older adults at 0 Hz and 0.66 Hz. Asterisk (*) indicates significant difference (P<0.05) between young and older adults.
Mentions: For the absolute power spectrum, the age×visual feedback angle interaction approached significance (F2,24 = 3.1, P = 0.06; Figure 5A). Visual inspection of the data demonstrated that magnification of visual feedback increased power below 1 Hz in older adults and decreased power below 1 Hz for young adults. The age main effect (P = 0.68) and the age×frequency bin interaction were not significant (P = 0.82). For the normalized power spectrum of force, there was a significant age×frequency bin interaction (F6, 108 = 2.59, P<0.05; Figure 5B). The interaction indicated that older adults compared with young adults exhibited greater relative power from 0 to 0.16 Hz and lesser relative power from 0.66 to 0.83 Hz under all visual feedback conditions. Post hoc analyses indicated that older adults compared with young adults exhibited greater power at 0 Hz (/t18/ = 2.6, P<0.01) 0.16 Hz (/t18/ = 1.5, P = 0.07) and lesser power from 0.66 Hz (/t18/>1.9, P<0.05).

Bottom Line: Older adults demonstrated a greater increase in the variability of force with magnification of visual feedback compared with young adults (P = 0.05).Furthermore, older adults exhibited differential force modulation of frequencies below 1 Hz compared with young adults (P<0.05).Specifically, older adults exhibited greater normalized power from 0-0.16 Hz and lesser normalized power from 0.66-0.83 Hz.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, USA.

ABSTRACT
Oscillations in force output change in specific frequency bins and have important implications for understanding aging and pathological motor control. Although previous studies have demonstrated that oscillations from 0-1 Hz can be influenced by aging and visuomotor processing, these studies have averaged power within this bandwidth and not examined power in specific frequencies below 1 Hz. The purpose was to determine whether a differential modulation of force below 1 Hz contributes to changes in force control related to manipulation of visual feedback and aging. Ten young adults (25±4 yrs, 5 men) and ten older adults (71±5 yrs, 4 men) were instructed to accurately match a target force at 2% of their maximal isometric force for 35 s with abduction of the index finger. Visual feedback was manipulated by changing the visual angle (0.05°, 0.5°, 1.5°) or removing it after 15 s. Modulation of force below 1 Hz was quantified by examining the absolute and normalized power in seven frequency bins. Removal of visual feedback increased normalized power from 0-0.33 Hz and decreased normalized power from 0.66-1.0 Hz. In contrast, magnification of visual feedback (visual angles of 0.5° and 1.5°) decreased normalized power from 0-0.16 Hz and increased normalized power from 0.66-1.0 Hz. Older adults demonstrated a greater increase in the variability of force with magnification of visual feedback compared with young adults (P = 0.05). Furthermore, older adults exhibited differential force modulation of frequencies below 1 Hz compared with young adults (P<0.05). Specifically, older adults exhibited greater normalized power from 0-0.16 Hz and lesser normalized power from 0.66-0.83 Hz. The changes in force modulation predicted the changes in the variability of force with magnification of visual feedback (R(2) = 0.80). Our findings indicate that force oscillations below 1 Hz are associated with force control and are modified by aging and visual feedback.

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